The disclosure of Japanese Patent Application No. 2002-53068 filed on Feb. 28, 2002 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
This invention relates to an operation control of an internal combustion engine for a vehicle, and particularly to an operation control method when stopping the operation of the internal combustion engine for the vehicle.
2. Description of Related Art
Fuel supply is stopped when stopping the operation of an internal combustion engine. In this case, in many of the current internal combustion engines, particularly in those for vehicles, the fuel supply is finally controlled by a fuel injection valve. Therefore, fuel supply may be stopped such that, after the engine stop is determined, the fuel injection valve is not opened at the next fuel injection timing which is synchronized with an operation cycle of the internal combustion engine. However, some of the fuel is adhered to a wall of a combustion chamber of the internal combustion engine even after the exhaust stroke. Particularly in a port injection type internal combustion engine in which the fuel injection valve injects fuel into an intake port, a large amount of fuel is constantly adhered to a wall surface of the intake port during operation of the engine. Accordingly, even if opening of the fuel injection valve is stopped so as to stop the engine, while the engine keeps rotating under its own inertia for a while, fuel removed from the wall surface is added to the intake air that is taken into a combustion chamber in accordance with such engine rotation.
Stopping of an internal combustion engine, particularly that of an internal combustion engine for a vehicle, has been executed by turning off an ignition switch to shut off all power supplies simultaneously including a fuel injection valve, a fuel pump for supplying the fuel to the fuel injection valve, and in the case of a gasoline engine, an ignition system for igniting an air-fuel mixture. However, in recent vehicles (such as hybrid vehicles and economy-running vehicles) equipped with a vehicle operation control system based on a microcomputer, it is possible to execute any automatic power processing by the vehicle operation control system even after the ignition switch is tuned off. In the hybrid vehicles and economy-running vehicles, the operation of the internal combustion engine is stopped, not only when the ignition switch is turned off, but also as necessary by a control of the vehicle operation control system. Therefore, the following art is suggested in Japanese Patent Laid-Open Publication No. 2000-337238. In a multi-cylinder internal combustion engine, even after the fuel injection to each cylinder is stopped based on an operation stop command, the ignition system is operated and stopping of the ignition system is retarded until all ignition signals, each of which corresponds to an air-fuel mixture of each cylinder formed by the fuel injected immediately before the stop of the fuel injection, are output. Thereafter, the ignition signals are stopped.
As is described in the aforementioned publication, by retarding the stopping of the operation of the ignition system relative to the stopping of the fuel supply when stopping the engine, the air-fuel mixture formed by the fuel injected immediately before the stop of the fuel injection and the fuel adhered to the wall surface can certainly be burned. In this case, however, combustion of the air-fuel mixture carried out due to the extended operation of the ignition system becomes lean combustion with a lean mixture, and thus a large amount of NOx may be generated. Since most of the current internal combustion engines for vehicles have a catalyst for purifying NOx in their respective exhaust system, it may suffice if NOx generated by the aforementioned lean combustion is processed by an exhaust purifying catalyst. Nevertheless, when exhaust gas caused by lean combustion is brought into the catalyst, an NOx purification rate of the catalyst is reduced, and NOx may be discharged without being purified. This issue is particularly critical to those vehicles such as hybrid vehicles and economy-running vehicles whose engine is stopped frequently.
On the other hand, when stopping the engine, in a case where unburned composition such as HC and CO is discharged to the exhaust system and oxidized in an oxidation catalyst and a three-way catalyst without burning the fuel removed from the wall surface extending from the intake port to the combustion chamber of the internal combustion engine by retarding stopping of the ignition system as described in the aforementioned Japanese Patent Laid-Open Publication No. 2000-337238, a large amount of heat is generated in the catalyst, and thus the catalyst may deteriorate due to overheating. Furthermore, in any case, some of the fuel adhered to the wall surface extending from the intake port to the combustion chamber of the internal combustion engine is removed from the wall surface during cranking for restarting the internal combustion engine and then added to the intake air. Of the fuel removed from the wall surface, those removed before the start of combustion during initial cranking is directly discharged from an exhaust port and carried to the catalyst.
As described above, a problem regarding exhaust gas purification caused by adherence of fuel to the wall surface extending from the intake port to the combustion chamber of the internal combustion engine in relation to an engine stop, particularly to a temporary stop of the engine which occurs frequently in a hybrid vehicle and an economy-running vehicle, has two conflicting aspects: when the fuel removed from the wall surface is burned in the engine, the amount of NOx generated by lean combustion may be increased, whereas when the fuel removed is oxidized in the catalyst, the catalyst may be overheated.
It is an object of the invention to solve, while overcoming the aforementioned conflicting aspects, a problem of exhaust gas purification caused in relation to adherence of fuel to a wall surface extending from an intake port to a combustion chamber of the internal combustion engine as well as an engine stop, particularly a temporary stop of the engine in a hybrid vehicle and an economy-running vehicle.
A first aspect of the invention relates to a control method of an internal combustion engine for a vehicle. This method includes the following steps of: determining whether an operation of the internal combustion engine should be stopped; executing, when it is determined that the operation of the internal combustion engine should be stopped, a fuel adherence reduction operation for reducing the amount of fuel adhered to a wall surface extending from an intake port to a combustion chamber of the internal combustion engine; and stopping supply of the fuel to the internal combustion engine after the fuel adherence reduction operation is executed.
A second aspect of the invention relates to an internal combustion engine operation control system for a vehicle. This system includes a fuel supply system for supplying fuel to the internal combustion engine, and a controller for controlling the fuel supply system. The controller determines whether an operation of the internal combustion engine should be stopped. If it is determined that the operation of the internal combustion engine should be stopped, the controller executes a fuel adherence reduction operation for reducing the amount of fuel adhered to a wall surface extending from an intake port to a combustion chamber. Furthermore, the controller controls the fuel supply system so as to stop supply of the fuel to the internal combustion engine, after executing the fuel adherence reduction operation.
xe2x80x9cAn operation state of the vehicle is detected, and the internal combustion engine is automatically stopped based on the detected operation statexe2x80x9d does not include xe2x80x9cnormal stopping of the internal combustion engine by turn-off of an ignition switch by a driver.xe2x80x9d